The overall goals of this project are to use electrophysiological methods to: (i) determine the membrane mechanisms which oxyntic (OC, acid-secreting) and surface epithelial (SEC, mucus- secreting) cells of the gastric fundus use to actively transport H, Cl, Na and HC03: and (ii) characterize the properties of the paracellular shunt. Because SECs of fundus and the cells of antrum have very similar transport properties, measurements will also be extended to the antrum. The isolated Necturus gastric mucosa and antrum will be used because they exhibit the same ionic transport properties as their mammalian counterparts yet they are histologically simpler, have larger cells and are much more robust in vitro. A vibrating probe which measures small extracellular currents will be used to determine the conductance properties of the SECs and OCs individually. Standard microelectrodes are used to impale both SECs and OCs and obtain membrane potential measurements. The vibrating probe and microelectrodes will be used in combination to obtain quantitative measurements of the conductance properties of the mucosal and serosal membranes and shunts (between cells) of the two cell types. Preliminary data indicate that SECs and OCs have very different membrane transport and conductance properties and also different shunts. Double-barreled ion selective electrodes will be used to determine intracellular (K), (Cl), (Na) and pH in the steady state and also to assess the non-conductive movements of ions via cotransporters (e.g. KCl symport) and exchangers (e.g. Cl/HC03 or Na/H antiport). Using these techniques the permeability, conductive and transport properties of the mucosal and serosal membranes of OCs and SECs and SECs to Na+, K+, Cl- HC03 and H+ will be determined. Also, the conductance properties of the shunts between OCs and between SECS can be determined. This information will be of obvious importance for our overall knowledge of how the stomach works. Also, since the "barrier" function of the stomach must somehow be related to the ability of the cells and shunt to exclude H+, this work should also yield useful information about this question.